Nematic liquid crystalline compounds

ABSTRACT

A compound of the general formula ##STR1## wherein A denotes a substituted ring structure represented by the formula ##STR2## the substituent R denotes a linear alkyl group having 1 to 9 carbon atoms, and the cyclohexane rings are both arranged in a trans(equatorial-equatorial)-form.

This is a division of application Ser. No. 546,534, filed Oct. 28, 1983,now U.S. Pat. No. 4,551,280.

This invention relates to novel nematic liquid crystalline compoundswhich are 3-fluoro-4-cyanophenol derivatives useful as electro-opticaldisplay materials.

The novel nematic liquid crystalline compounds provided by thisinvention are represented by the following formula ##STR3## wherein Adenotes a substituted ring structure represented by the formula ##STR4##the substituent R denotes a linear alkyl group having 1 to 9 carbonatoms, and the cyclohexane rings are both arranged in atrans(equatorial-equatorial)form.

Typical liquid crystal display cells include, for example, a fieldeffect mode cell proposed by M. Schadt et al. (Applied Physics Letters,18, 127-128 (1971)], a dynamic scattering mode cell proposed by G. H.Heilmeier [Proceedings of the I.E.E.E., 56, 1162-1171 (1968)], and aguest-host mode cell proposed by G. H. Heilmeir [Applied PhysicsLetters, 13, 91 (1968)] or D. L. White (Journal of Applied Physics, 45,4718 (1974)].

Liquid crystalline materials used in the field effect mode cell, aboveall, a TN mode cell are required to have various properties. A lowoperating voltage is one of the important properties. In general, thedecrease in the operating voltage of liquid crystal display cellscorresponds to the decrease in the threshold voltage (Vth) of liquidcrystals. The threshold voltage (Vth) of liquid crystals has thefollowing relation between an anisotropy (Δε) of dielectric constant andan elastic constant K. ##EQU1##

A liquid crystalline compound to decrease the threshold voltage (Vth)is, for example, a compound of the following formula having a highanisotropy (Δε). ##STR5## Such a compound has however a low N-Itransition temperature, narrowing an operating temperature range ofliquid crystals. Moreover, a compound of the following formula having ahigh N-I transition temperature and a relatively high anisotropy (Δε)increases a threshold voltage (Vth) when mixed with a TN mode liquidcrystalline composition because the elastic constant K is also veryhigh.

The compounds of the formula (I) according to this invention are novelcompounds with these properties improved. That is, the compounds of theformula (I) are mixed with one or more of other nematic liquidcrystalline compounds to increase the N-I transition temperature whiledecreasing the threshold voltage (Vth). Thus, the use of the compoundsof the formula (I) enables the formation of TN mode liquid crystallinecompositions wherein the upper limit of the temperature range of thenematic phase is high and the threshold voltage (Vth) is low.

The compounds of the formula (I) in this invention can be produced bythe 2-step reaction schematically shown below. ##STR6## wherein Adenotes the aforesaid substituted ring structure.

In the first step, a compound of the formula (i) is reacted with ahalogenating agent to provide a compound of the formula (ii) wherein Xis a halogen atom. In the compound of the formula (ii), X is preferablya chlorine atom. Thionyl chloride may be used as the halogenating agent.The reaction is carried out at a reflux temperature of the reactionmixture and at normal pressure. It is unnecessary to isolate thecompound of the formula (ii) from the mixture formed by the reaction,and it is sufficient to remove excess halogenating agent alone.

In the second step, the crude compound of the formula (ii) afforded inthe first step is reacted with a compound of the formula (iii) in aninert organic solvent. Examples of the inert organic solvent include,for example, diethyl ether, tetrahydrofuran, dimethylformamide andbenzene. In order to remove hydrogen halides liberated during thereaction from the reaction system, it is advisable to contain basicsubstances such as pyridine, tertiary amines, etc. in said inert organicsolvent. The reaction is carried out at temperatures ranging from roomtemperature to a reflux temperature of the reaction mixture and atnormal pressure. The final compound of the formula (I) can be isolatedby subjecting the reaction product to a series of purifying treatmentssuch as solvent extraction, water-washing, drying, recrystallization,and so forth.

The transition temperatures of the typical compounds represented by theformula (I) which are produced as above are shown in Table 1. In table1, C represents a crystalline phase; N, a nematic phase; and I, anisotropic liquid phase.

                  TABLE 1                                                         ______________________________________                                         ##STR7##                                                                                       Transition                                                                    temperature (°C.)                                     No.poundCom-                                                                        A                                                                                               ##STR8##                                                                                 ##STR9##                                  ______________________________________                                         1                                                                                   ##STR10##        88         172                                         2                                                                                   ##STR11##        101        203                                         3                                                                                   ##STR12##        81         192                                         4                                                                                   ##STR13##        91         195                                         5                                                                                   ##STR14##        85         178                                         6                                                                                   ##STR15##        80         167                                         7                                                                                   ##STR16##        64         157                                         8                                                                                   ##STR17##        60         160                                         9                                                                                   ##STR18##        57         148                                        10                                                                                   ##STR19##        53         142                                        11                                                                                   ##STR20##        129        206                                        12                                                                                   ##STR21##        104        207                                        13                                                                                   ##STR22##        92         197                                        14                                                                                   ##STR23##        84         191                                        ______________________________________                                    

The compounds of the formula (I) in accordance with this invention arenematic liquid crystalline compounds having a strong positive dielectricanisotropy and therefore can be used, for example, as materials forfield effect mode display cells in the form of mixtures with othernematic liquid crystalline compounds having a negative or weak positivedielectric anisotropy or other nematic liquid crystalline compoundshaving a strong positive dielectric anisotropy.

Typical examples of nematic liquid crystalline compounds which canpreferably be used in admixture with the compounds of the formula (I)include phenyl 4,4'-substituted benzoates, phenyl 4,4'-substitutedcyclohexanecarboxylates, biphenyl 4,4'-substitutedcyclohexanecarboxylates, 4'-substituted phenyl 4(4-substitutedcyclohexanecarbonyloxy)benzoates, 4'-substituted phenyl 4(4-substitutedcyclohexyl)benzoates, 4'-substituted cyclohexyl 4(4-substitutedcyclohexyl)benzoates, 4,4'-biphenyl, 4,4'-phenylcyclohexane,4,4'-substituted terphenyl, 4,4'-biphenylcyclohexane, and2(4'-substituted phenyl)-5-substituted pyrimidine.

Table 2 indicates the N-I points and threshold voltages (Vth) measuredfor mixed liquid crystals composed of 80% by weight of matrix liquidcrystals (A) now in widespread use as a nematic liquid crystallinematerial having excellent characteristics for time multiplex drive and20% by weight of compounds Nos. 1 to 14 of the formula (I) respectivelyindicated in Table 1. The same table also illustrates the N-I point andthreshold voltage measured for the matrix liquid crystals (A) forcomparison.

The matrix liquid crystals (A) comprises ##STR24##

                  TABLE 2                                                         ______________________________________                                                            Threshold                                                              N-I point                                                                            voltage (Vth)                                                          (°C.)                                                                         (V)                                                       ______________________________________                                        (A)            54.0     1.65                                                  (A) + (No. 1)  76.2     1.41                                                  (A) + (No. 2)  82.4     1.42                                                  (A) + (No. 3)  80.2     1.43                                                  (A) + (No. 4)  80.8     1.44                                                  (A) + (No. 5)  77.4     1.46                                                  (A) + (No. 6)  75.2     1.48                                                  (A) + (No. 7)  72.6     1.46                                                  (A) + (No. 8)  73.0     1.46                                                  (A) + (No. 9)  71.6     1.49                                                  (A) + (No. 10) 71.2     1.49                                                  (A) + (No. 11) 82.9     1.40                                                  (A) + (No. 12) 82.8     1.40                                                  (A) + (No. 13) 81.9     1.43                                                  (A) + (No. 14) 81.2     1.44                                                  ______________________________________                                    

From the data shown in Table 2 above, it follows that the compounds ofthe formula (I) can decrease the threshold voltage (Vth) of mixed liquidcrystals and besides increase the N-I point thereof. Thus, the highpractical value of the compounds of the formula (I) resides in that themixed liquid crystals having the low threshold voltage (Vth) and highN-I points can be obtained.

The superiority provided by the compounds of this invention isillustrated by the following Comparative Examples.

FIGS. 1, 2 and 3 attached hereto are graphs that compare properties ofmixed liquid crystals prepared in the Comparative Examples 1, 2 and 3.

COMPARATIVE EXAMPLE 1

A known compound of the following formula ##STR25## which has a chemicalstructure similar to the compound of the formula (I) in accordance withthis invention and is widely used in order to increase the N-I point ofmixed liquid crystals was mixed in various proportions with the matrixliquid crystals (A) described above to provide a large number of mixedliquid crystals containing the known compound.

Likewise, one compound of this invention represented by the followingformula ##STR26## was mixed in various proportions with the matrixliquid crystals (A) to provide a large number of mixed liquid crystalscontaining the compound of this invention.

With respect to the thus obtained mixed liquid crystals, the thresholdvoltage (Vth) and N-I point were measured and the resulting data wereplotted in FIG. 1.

COMPARATIVE EXAMPLE 2

A known compound of the following formula ##STR27## which has a chemicalstructure similar to the compound of the formula (I) in accordance withthis invention and is widely used in order to increase the N-I point ofmixed liquid crystals was mixed in various proportions with the matrixliquid crystals (A) described above to provide a large number of mixedliquid crystals containing the known compound.

Likewise, one compound of this invention represented by the followingformula ##STR28## was mixed in various proportions with the matrixliquid crystals (A) to provide a large number of mixed liquid crystalscontaining the compound of this invention.

With respect to the matrix liquid crystals (A) and mixed liquid crystalsthus obtained, the threshold voltage (Vth) and N-I point were measuredand the resulting data were plotted in FIG. 2.

COMPARATIVE EXAMPLE 3

A known compound of the following formula ##STR29## which has a chemicalstructure similar to the compound of the formula (I) in accordance withthis invention and is widely used in order to increase the N-I point ofmixed liquid crystals was mixed in various proportions with the matrixliquid crystals (A) described above to afford a large number of mixedliquid crystals containing the known compound.

Likewise, one compound of this invention represented by the followingformula ##STR30## was mixed in various proportions with the matrixliquid crystals (A) to afford a large number of mixed liquid crystalscontaining the compound of this invention.

With respect to the matrix liquid crystals and mixed liquid crystalsthus obtained, the threshold voltage (Vth) and N-I point were measuredand the resulting data were plotted in FIG. 3.

From the facts indicated in FIGS. 1 to 3, it can be seen that in themixed liquid crystals containing the typical known compounds similar inchemical structure to those of this invention, as the N-I pointincreases, the threshold voltage increases, whereas in the mixed liquidcrystals containing the compounds of the formula (I) in accordance withthis invention, as the N-I point increases, the threshold voltagedecreases.

The following Examples illustrate production of the compounds in thisinvention specifically.

EXAMPLE 1

Thionyl chloride (30 cc, 0.0052 mole) was added to 1.2 g (0.0052 mole)of a compound of the following formula. ##STR31## The mixture wasreacted for 30 minutes under reflux and excess thionyl chloride was thendistilled off. Subsequently, 0.70 g (0.0052 mole) of the followingformula ##STR32## was added to the resulting reaction product, and 30 ccof toluene and 1 g of pyridine were further added. They were reacted for30 minutes under reflux. The reaction liquid was then washed with 1%hydrochloric acid and water to render said liquid neutral. Toluene wasthen distilled off from the reaction liquid. The resulting reactionproduct was recrystallized from ethanol to afford 1.0 g (0.0029 mole) ofa compound of the following formula. ##STR33##

Yield: 54%

Transition temperatures:

88° C. (C→N)

172° C. (N⃡I)

EXAMPLE 2

A compound of the following formula was produced as in Example 1.##STR34##

Yield: 70%

Transition temperatures:

101° C. (C→N)

203° C. (N⃡I)

EXAMPLE 3

A compound of the following formula was produced as in Example 1.##STR35##

Yield: 72%

Transition temperatures:

81° C. (C→N)

192° C. (N⃡I)

EXAMPLE 4

A compound of the following formula was produced as in Example 1.##STR36##

Yield: 69%

Transition temperatures:

91° C. (C→N)

195° C. (N⃡I)

EXAMPLE 5

A compound of the following formula was produced as in Example 1.##STR37##

Yield: 70%

Transition temperatures:

85° C. (C→N)

178° C. (N⃡I)

EXAMPLE 6

A compound of the following formula was produced as in Example 1.##STR38##

Yield: 74%

Transition temperatures:

80° C. (C→N)

167° C. (N⃡I)

EXAMPLE 7

Thionyl chloride (30 cc) was added to 0.89 g (0.00342 mole) of acompound of the following formula ##STR39## and the mixture was reactedfor 30 minutes under reflux, followed by distilling off excess thionylchloride. To the resulting reaction product were then added 0.47 g(0.00342 mole) of a compound of the following formula ##STR40## 30 cc oftoluene and 1 g of pyridine. They were reacted under reflux. Thereaction liquid was then washed with 1% hydrochloric acid and water torender said liquid neutral. Subsequently, toluene was distilled off fromthe reaction liquid. The resulting reaction product was recrystallizedfrom ethanol to obtain 0.89 g (0.00236 mole) of a compound of thefollowing formula. ##STR41##

EXAMPLE 8

A compound of the following formula was produced as in Example 7.##STR42##

Yield: 75%

Transition temperatures:

64° C. (C→N)

157° C. (N⃡I)

EXAMPLE 9

A compound of the following formula was produced as in Example 7.##STR43##

Yield: 70%

Transition temperatures:

57° C. (C→N)

148° C. (N⃡I)

EXAMPLE 10

A compound of the following formula was produced as in Example 7.##STR44##

Yield: 65%

Transition temperatures:

53° C. (C→N)

142° C. (N⃡I)

EXAMPLE 11

Thionyl chloride (50 cc) was added to 2.26 g (0.01 mole) of a compoundof the following formula ##STR45## and the mixture was reacted for 30minutes under reflux, followed by distilling off excess thionylchloride. Subsequently, to the resulting reaction product were added1.37 g (0.01 mole) of a compound of the following formula ##STR46## 50cc of toluene and 2 g of pyridine. They were reacted under reflux. Thereaction liquid was washed with 1% hydrochloric acid and water to rendersaid liquid neutral, and toluene was then distilled off from thereaction liquid. The resulting reaction product was recrystallized fromethanol to obtain 2.8 g (0.008 mole) of a compound of the followingformula. ##STR47##

Yield: 80%

Transition temperatures:

129° C. (C→N)

206° C. (N⃡I)

EXAMPLE 12

A compound of the following formula was produced as in Example 11.##STR48##

Yield: 75%

Transition temperatures:

104° C. (C→N)

207° C. (N⃡I)

EXAMPLE 13

A compound of the following formula was produced as in Example 11.##STR49##

Yield: 68%

Transition temperatures:

92° C. (C→N)

197° C. (N⃡I)

EXAMPLE 14

A compound of the following formula was produced as in Example 11.##STR50##

Yield: 72%

Transition temperatures:

84° C. (C→N)

191° C. (N⃡I)

What is claimed is:
 1. A compound of the general formula ##STR51##wherein A denotes a substituted ring structure represented by theformula ##STR52## the substituent R denotes a linear alkyl group having1 to 9 carbon atoms.
 2. The compound of the general formula as set forthin claim 1 wherein R is a linear alkyl group having from 2 to 5 carbonatoms.
 3. The compound of the general formula as set forth in claim 1wherein R is C₃ H₇.
 4. The compound of the general formula of claim 1wherein R is C₅ H₁₁.